First and foremost; the Moments of Silence
1927: Walter Johnson's 110th Shutout
On Memorial Day in 1927, the "Big Train" got the last of his 110 career shutouts, a 3-hit performance against the Red Sox. The active leader in shutouts is Clayton Kershaw with 15.
1951: Willie Mays Gets First Career Hit - a Home Run
Starting his career going 0-for-12 in his first three games, the "Say Hey Kid" got his first hit, a home run, on Memorial Day in 1951. It was off Braves pitcher, and co-Future Hall of Famer, Warren Spahn.
1953: Max Surkont Strikes Out 8 Straight Batters
Pitching for the Milwaukee Braves, Max Surkont set a then MLB record of eight straight strikeouts. His record would be broken by Mets' Tom Seaver in 1970.
1956: Dale Long's Eight Game Home Run Streak
On Memorial Day in 1956, Pirates first baseman Dale Long homered in his 8th straight game. Long's record would be tied by Don Mattingly in 1987, and again by Ken Griffey Jr. in 1993.
Later that same day, game two of the doubleheader, Wilbur Wood tossed a four-hit shutout - getting his second "W" of the day.
2000: Randy Velarde's Unassisted Triple Play
Oakland Athletics second baseman Randy Velarde completed the rare unassisted triple play against the New York Yankees, on Memorial Day in 2000. Velarde caught a line drive from Shane Spencer for out #1, he tagged Jorge Posada for out #2 and stepped on second base for out #3 (Tino Martinez was in motion, the first out made it a force play at second base).
2004: Ken Griffey Jr. Passes Lou Gehrig
"The Kid" blasted his 494th career homer in a game against the Marlins. That home run put Griffey into 20th on the all-time list at that point. He would finish with 630, the 5th most ever.
2013: Justin Verlander Strikesout 13
On Memorial Day in 2013, Tigers' ace Justin Verlander struckout 13 Pittsburgh Pirates over seven innings, leading to his 6th win of the year.
Last, but certainly not least..
World War II Veterans Throw Out First Pitches